The coloration in the living frogs is highly variable due to extreme metachrosis. Individuals of this species are capable of changing the dorsal coloration from green to brown in a short period of time. Both green and brown individuals have been found active at night. Usually those individuals found hiding by day are brown. One individual from Finca La Sumbadora, Panama (now KU 91914), was kept alive in the laboratory for nearly one month. This individual usually was pale green with tan dorsal markings at night and tan with pale green markings by day. On occasion the pale green dorsal markings were boldly outlined by bright dark green. In living individuals from throughout the range of the species the iris is a bronze color, darkest medially with fine black reticulations. _Natural History._--_Smilisca phaeota_ inhabits humid lowland tropical forest and seldom ascends the foothills to more than 1,000 meters. The rather equable climatic conditions, especially more or less evenly distributed rainfall throughout the year, permit this frog to be active most of the year. Dunn (1931:413) reported males calling on Barro Colorado Island, Panama, in February and in July, and Breder (1946:416) noted calling individuals in the Chucanaque drainage of Darien, Panama in January, March, July, August and October and in Costa Rica in April through August inclusively. Calling males were found at Bonanza, Nicaragua in March and in July. At all times of year the usual daytime retreats for these frogs are near water; the frogs have been found in elephant ear plants (_Xanthosoma_) and in bromeliads; occasional individuals have been found sitting on shaded branches of bushes and trees. None has been observed on the ground or beneath ground-cover by day. The length of the breeding season cannot be determined definitely. The earliest date on which eggs have been found is May 23; Gaige, Hartweg, and Stuart (1937:5) reported a gravid female taken at El Recreo, Nicaragua, in September, and we have a gravid female taken at Almirante, Panama, in March. Males usually call from secluded spots at the edge of water. All calling males that we observed were on the ground within a few centimeters of the water. The males usually are hidden beneath an overhanging leaf or some other cover; they definitely do not sit in the open like _Smilisca baudini_. Most calling males and clasping pairs have been found at the edges of small pools or shallow ditches, although occasional individuals are found at the edges of large ponds or streams. The breeding call consists of one or two moderately short, low-pitched notes (duration 0.33 to 0.42 seconds), repeated at intervals of about 20 seconds to several minutes. Each note is a low, vibrant "wauk," having 100 to 130 pulses per second and a dominant frequency of 330 to 420 cycles per second (Pl. 10C).